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Enhancement of calcium oxide on hydrogen production and degradation of polylactic acid microplastics in anaerobic fermentation
Summary
Polylactic acid (PLA) is promoted as an eco-friendly biodegradable plastic, but under conventional anaerobic conditions it degrades slowly and can accumulate as microplastics in sewage treatment systems. Adding calcium oxide (CaO) to anaerobic fermentation reactors both accelerated PLA microplastic degradation and boosted hydrogen gas production as an energy byproduct. The mechanism involves CaO creating mildly alkaline conditions that help break PLA's ester bonds while buffering against acid buildup that normally inhibits microbes. This suggests that chemical additives could make biological microplastic treatment more practical in wastewater settings while recovering renewable energy simultaneously.
Anaerobic fermentation provides a sustainable route for microplastic (MP) degradation with concurrent energy recovery. In this study, calcium oxide (CaO) was applied as a buffering agent to enhance hydrogen production and promote the degradation of polylactic acid (PLA) microplastics during anaerobic fermentation. Inocula from anaerobic and anoxic tanks were used to evaluate hydrogen production, metabolite transformation, and PLA degradation under varying CaO dosages. CaO addition significantly increased cumulative hydrogen yield and volatile fatty acid (VFA) production while accelerating lactic acid conversion. Mechanistically, CaO facilitated PLA degradation through weak-alkaline-assisted ester bond hydrolysis and mitigated excessive acidification by neutralizing accumulated VFAs, thereby stabilizing system pH. This buffering effect promoted the enrichment of hydrogen-producing and alkali-tolerant microorganisms and redirected metabolic pathways toward acetate-butyrate fermentation, collectively enhancing hydrogen production. At 2 g/L CaO, cumulative hydrogen yields increased by 78.52% and 50.56% in the anaerobic and anoxic systems, respectively, while PLA weight loss increased by 67.45% and 82.34%. These results demonstrate a synergistic chemical-biological mechanism by which CaO enhances microplastic degradation and biohydrogen recovery in anaerobic systems.